McConnell's reasoning at the time? It was important for the Senate to "give the people a voice in the filling of this vacancy" by waiting until the new president took office.

"The American people may well elect a president who decides to nominate Judge Garland for Senate consideration," he said. "The next president may also nominate someone very different. Either way, our view is this: Give the people a voice."

McConnell suggested in October that he would be open to filling a Supreme Court vacancy in 2020, when Trump is up for re-election. The difference from 2016, when a Republican-controlled Senate blocked a Democratic president's nominee? Trump and the Senate, which confirms judges, are the same party, McConnell said last fall.

But McConnell never made that argument in 2016, when he wouldn't let the Senate even hold hearings on Garland. The only precedent the majority leader cited at the time was the "Biden rule."

In 2016, McConnell used Biden's argument, which was never formally adopted, to justify blocking Garland – even after the election when Obama had two months left in office.

Now, McConnell is also making the argument that it's been tradition since 1880 that a Senate of one party does not fill a Supreme Court vacancy with the nominee from the president of another if the opening is "created in the presidential year."

But in February 1988, the last year of Republican Ronald Reagan's presidency, the Democratic-controlled Senate voted 97-0 to confirm Anthony Kennedy to the high court. Kennedy's nomination had been announced in November 1987.

McConnell followed up his remarks by issuing a fundraising appeal Wednesday, saying he was "proud" to have blocked Garland's confirmation in 2016.

"If there's a vacancy on the Supreme Court in 2020, I will proudly confirm President Trump’s nominee," McConnell wrote. "Sure, the Left and their allies in the media will go crazy. The Democrats will raise MILLIONS to defeat me. That won’t stop us from putting another conservative Justice on the Supreme Court."

There are no vacancies on the nine-member court. But its two oldest members – Ruth Bader Ginsburg, 86, and Stephen Breyer, 80 – are two of the four liberal members of the court. If one steps down or can no longer serve, Trump would have a chance to solidify the conservative majority for decades to come.

Senate Majority Leader Mitch McConnell of Ky. speaks to reporters as he walks out of the Senate Chamber on Capitol Hill in January.(Photo: Andrew Harnik, AP)

Would Senate confirm a justice in 2020?

With Republicans controlling the Senate through at least Jan. 3, 2021, Trump's choice would have a good chance of winning approval. The only sticking point is whether McConnell's fellow Republicans, notably Judiciary Committee Chairman Lindsey Graham, R-S.C., would oppose moving forward in an election year.

Graham, whose committee holds Supreme Court confirmation hearings, said last year he would hold off on a confirmation if a vacancy occurred in 2020.

Supreme Court Associate Justice Clarence Thomas and his wife Virginia Thomas arrive for the funeral of fellow Associate Justice Antonin Scalia at the Basilica of the National Shrine of the Immaculate Conception in 2016. Chip Somodevilla, Getty Images

Supreme Court Associate Justices Ruth Bader Ginsburg and Antonin Scalia pose with members of the cast of "Ariadne auf Naxos" following a performance at the Washington National Opera in 1994. Stephen R. Brown, AP

Supreme Court Associate Justice Ruth Bader Ginsburg prepares to administer the Oath of Allegiance to candidates for U.S. citizenship at the New York Historical Society on April 10, 2018 in New York City. Spencer Platt, Getty Images

Supreme Court Associate Justice Stephen Breyer descends a stairway at the French Cultural Center in Boston followed by center members Mary Ann Sorel and her husband Pierre Sorel in 2017. Steven Senne, AP

Supreme Court Associate Justice Sonia Sotomayor, a diehard Yankees fan, talks with other fans in the "Judge's Chambers" before a game against the Boston Red Sox at Yankee Stadium in 2017. Rich Schultz, Getty Images

Supreme Court Associate Justice Sonia Sotomayor gestures while speaking with actress Eva Longoria Baston to discuss Sotomayor's life story and promote her new book during an event at George Washington University in March 2019. Pablo Martinez Monsivais, AP

Supreme Court Associate Justice Sonia Sotomayor appears with actress Eva Longoria Baston to discuss Sotomayor's life story and promote her new book during an event at George Washington University in March 2019. Pablo Martinez Monsivais, AP

Swearing in of Coloradan Neil M. Gorsuch as the newest member of the, United States Court Of Appeals For The Tenth Circuit, with his wife Louise Gorsuch, holding the bible, and his two daughters, Belinda Gorsuch age 4, and Emma Gorsuch age 6 on Nov. 20, 2006 in Denver. John Prieto, Denver Post via Getty Images

Brett Kavanaugh shakes hands with President George W. Bush after he was sworn in by Supreme Court Justice Anthony Kennedy to be a judge to the U.S. Circuit Court of Appeals for the District of Columbia as his wife Ashley looks on during a swearing-in ceremony at the Rose Garden of the White House June 1, 2006 in Washington, DC. Kavanaugh was confirmed by the Senate with a vote of 57 to 36. Alex Wong, Getty Images